New to par car. I have what I believe is a 1990 (3L-200099-D0). I just picked this cart up. The batteries all charge (6.2v on average after charge and 12hr of rest time). The cart has about 37.5 volts while driving and will load down drop down to about 28v. On flat ground it runs great (for what it is) with good power and torque. My problem happens when going up hills. The cart absolutely falls on its face. It never fully comes to a stop, there is always some pull going up hill it's just extremely slow. I checked with a meter and the battery pack never drops below 28v. I individually put the test on each battery and drove it. Each battery starts off at 6.2v and the lowest drop is about 5.2v for each battery. This is my first electric cart so I'm lost with what to check next. I found the potentiometer and there is a black wire that is cut and not connected to anything. Its NOT in the wire harness for the potentiometer. I've included pictures. Just above it there is a main harness with a wire that has a butt connector on it. Unsure if they go together or not. Didn't want to connect and fry something.
Any help would be great and much appreciated.
The cart runs great when on flat ground even after cresting the hill and going back to flat surface. The water levels are correct in the batteries.

if i,m reading this right sounds as tho your batteries are pretty much worn out think they should read 40 volts total and over when full charged and 7 or close for each battery,,, go online and get a 36 volt charge chart and you will see what i,m saying,, or someone else may have another idea good luck

You're correct on the VIN showing a 1990, but your vehicle has the accelerator more closely to the 1991. The wiring for the 1991 shows that extra black wire (where someone has cut it out of the circuit) as a fused link. I attached photos from the 91 manuals showing that and the wiring diagram.

And I concur with karly's read on the batteries. A 36 volt pack fully charged should ride more closely to 40 or higher. You would want to also check specific gravity on each cell.

Ok awesome thanks everyone. I guess I should have looked that chart up first.
I'm gonna throw 6 new batteries in it, add the inline fuse and see what happens.
I have a perfectly running Yamaha g2 that I fixed up but its gas. More and more campgrounds won't allow the gas golf carts so I picked this Par Car up for few bucks.

Before you run out and buy new batteries you might want to have the batteries load tested. My cart, even with good batteries bogs down on hills to some degree and that's with a 48 system. Some of the hills on the golf course I need to do a running start or it doesn't even make it to the top. At first, this was a concern but I came to realize that the gearing was set up for cruising efficiency, not hill climbing.

A lot depends on what speed you're running on the flats and what speed it slows down too at the crest and how steep the grade. Check the speeds with a GPS speed app on your phone and let us know.

There is a possibility that you just have a normal condition that new batteries won't resolve.